The V8 Owners Forum -

What is the correct pressure rad cap please for my RV8 4.6?
My old cap perished.
It currently has a 15lb and runs at 80 deg all day long.
But the coolant does escape the cap. I notice it doesn't have a rubber seal, just a metal plate, I brought it from Halfords?

I have a new 20lb one with a seal, but will this damage the cooling system with too high pressure?

Thanks Mark.

There are many many cap designs...so ensure the cap design is correct for your specific application.


But 15psi will be fine, I see little need for a 20psi cap unless you intend running the engine very hot.

But it sounds more like you've had the wrong cap fitted regardless of pressure rating.

Does it have a rubber seal on the inner part? I'd be surprised if there was no rubber seal at all.


Chris.

Yes Chris. The smaller bit has the rubber seal and one way valve. The top 60mm is simply a flat steel plate.
Got rid now and a new one with 2 x rubber seals.
However, at 3am this morning I woke up suddenly realising what the issue was.
When I put the new thermostat in, I have accidentally been too exuberant with the silicone sealant on the gasket and it blocked the bypass hole and blocked the little wobbly thing on the thermostat. So when cold the water had no where to go and reversed back up the feed pipe from the header tank from the bottom hose and came out of the header tank. When hot no issue because stat was open.

Seems to have worked.

Good news!

Chris.